Tezzeret was born in Tidehollow, on Esper, one of the shards of Alara. Unlike most planeswalkers, Tezzeret has no surname. In fact, he didn't even have a name until, as a boy, he stabbed a bully with a shiv - tezzeret being the local slang for an improvised weapon. Tezzeret is a highly-intelligent gifted artificer. However, he has a rather explosive temper, and when he loses it, people tend to end up dead.
When he was seven years old, his mother was killed, run over by a guildmaster's carriage. That was when Tezzeret decided that he would do anything he could to become a powerful mage, so no one could ever take something from him again. To that end he began stealing small amounts of the rare, expensive and highly-in-demand magical alloy etherium, a metal that only a group called the Seekers of Carmot knew the secret to making. He was helped in this endeavor by discovering he had a natural talent for rhabdomancy, the magical ability to locate metal. With the money he earned from this, he joined the Machinist Guild, and at the age of 19, amputated his right arm, replacing it with an artificial limb made of etherium filigree. The guild immediately elevated Tezzeret to master status.
Using his newfound status, Tezzeret joined the Vectis City Academy, and applied for entry into the Seekers. In order to gain entry, he had to best Silas Renn in a dual, which he was unable to do. The Seekers denied him entry. Tezzeret worked hard to get a second chance, but kept being passed over. Finally, he had enough and broke into the Seeker's vault to steal the Codex Etherium...only to find that the pages were blank. The Seekers didn't know how to make etherium. No one did.
Unfortunately, this time Tezzeret got caught. When the Seekers tried to kill him to cover up their lies, his spark ignited, and he planeswalked to the shard of Grixis. There he met Nicol Bolas - who offered him power if he would work for Bolas.
For some unknown reason, Nicol Bolas appears to actually care about Tezzeret. Most of his minions find themselves discarded and killed if they fail him, rebel against him, or just outlive their usefulness. But Bolas has spent great effort and considerable rescources to bring Tezzeret back in line when he strays (which has happened multiple times).
Tezzeret, for his part, deeply resents Nicol Bolas for his role in creating the Seekers, as he spent much of his life working to become one, only to find that their teachings were all lies. But, Nicol Bolas did promise him power, and has delivered on that promise.
Tezzeret was placed in charge of one of Bolas' organisations, the Inifinite Consortium, which exploited the power vacuum on Ravnica in the aftermath of the original Ravnica storyline. He repaid Bolas by assassinating everyone who knew the Consortium answered to Bolas, and taking it for himself. It worked, for many years Tezzeret operated with impunity - until Liliana, who was secretly working for Nicol Bolas, manipulated him into starting a war with Jace Beleren. The war ended with Jace erasing Tezzzeret's mind, cutting off his etherium arm, and leaving him in the hands of the nezumi on the plane of Kamigawa.
Bolas managed to retrive Tezzeret and spent months rebuilding his mind and body. He then sent Tezzeret to New Phyrexia to keep an eye on the Phyrexians, and sabotage their leadership structure. At some point after this, he was ordered to relocate to Kaladesh, where he infiltrated the government (known as the Consulate) and was eventually appointed Grand Consul. He used his power to seize control of a powerful artifact Bolas needed - the Planar Bridge - and despite the fact that Jace and the Gatewatch blew it up, Tezzeret escaped with the core, allowing him to rebuild the Bridge, and later, use it to transport another powerful artifact - the Immortal Sun.
Both artifacts seem to be of great importance to Bolas' decade-spanning plans, though exactly what he plans on doing with them is still unclear. One thing is for sure, when Bolas enacts his endgame, Tezzeret will be right there too.
